This invention relates to a chair having a seat and a seatback in which the seat and the seatback can be tilted between a working position and a relaxing position, and a rotary damper which is suited to be used for the chair and others.
A conventional chair with a seatback is disclosed in Japanese Patent Application Laid-Open No. H06-253940. This chair with a seatback comprises a main frame disposed at an upper end of a support leg, a seatback frame whose forward end is turnably disposed at the main frame, thereby enabling the seatback, which is disposed at an upper part of a rear end side, can be tilted between a working position and a relaxing position, and a seat frame at which the seat is disposed. A rear end part of the seat frame is turnably connected to the seatback frame. On the other hand, a forward end part of the seat frame is connected to the main frame through a positive motion cam mechanism. The positive motion cam mechanism comprises a cam hole formed in the main frame, and a shaft portion disposed at the seat frame and movably engaged with said cam hole. When the rear end part of the seat frame is moved upward and downward in accordance with the turning motion of the seatback frame, the positive motion mechanism causes the entire seat frame to move in forward and backward, upward and downward directions and tiled in an upward and downward direction in accordance with the turning motion of the seat frame in upward and downward directions.
The chair with a seatback further comprises bias means for biasing the seat frame and the seatback frame from the relaxing position side towards the working position side. The bias means biases the seat and the seatback in a working position when a person is not sitting on the seat, but it allows the seat and the seatback to be tilted in the relaxing position side when he leans against the seatback, depending on the load acting on the seatback.
The above-mentioned conventional chair with a seatback has the following various problems. First, since the cam hole of the positive motion cam mechanism is required not only to move the seat frame in a forward and backward direction but also to displace and tilt the seat frame in an upward and downward direction, the length of the cam hole must be long in an upward and downward direction. Accordingly, the main frame is also required to be increased in length in its upward and downward direction in accordance with the length of the cam hole in an upward and downward direction. For this reason, the chair with a seatback is difficult to be made small in size.
Second, if a comparatively large load acts on the seatback when a biasing force of the bias means for biasing the seat and the seatback from a relaxing position side to a working position side is small, the seat and the seatback are tilted from the working position towards the relaxing position at a high speed. As a result, the person sitting on the chair gets such an anxiety that the chair may be fallen down. If the biasing force of the bias means is increased, there occurs such an inconvenience that when, for example, the user of the chair changes his attitude in the relaxing position and as a result, the load acting on the seatback is reduced, the seat and the seatback is turned back to the working position side against the user""s will.
Third, the seatback is supported on the main frame through a support arm but the conventional support arm is formed substantially as a rigid body. Accordingly, the seatback cannot be turned in a horizontal direction. For this reason, when the user turns backwards in a state in which he sits on the chair with a seatback, he cannot twist his body with his back kept contacted with the seatback and therefore, he must move his back forward from the seatback once.
The first form of the present invention is to solve the first problem and provides, therefore, a chair with a seatback comprising a main frame, a seat frame arranged at an upper part of the main frame, a seatback frame whose forward end part is connected to a forward end part of the main frame such that the forward end part can turn about a horizontal axis, thereby enabling a rear end part of the seatback frame to be tilted between a working position and a relaxing position, a displacement mechanism disposed between the rear end part of the seat frame and the seatback frame and adapted to displace the rear end part of the seat frame in an obliquely forward/backward direction in accordance with the turning motion of the seatback frame, and a positive motion cam mechanism for displacing the seat frame upward and downward, forward and backward and for tilting the seat frame upward and downward in corporation with the displacement mechanism, wherein the positive motion cam mechanism is disposed between the forward end part of the seat frame and the forward end part of the seatback frame.
In this case, it is preferred that the positive motion cam mechanism includes a cam hole and a shaft movably inserted in the cam hole in a longitudinal direction of the cam hole, one of the cam hole and the shaft is disposed at the seat frame and the other is disposed at the seatback frame. The cam hole is preferably disposed at the seatback frame.
It is preferred that the displacement mechanism includes a link connected at a lower end part thereof to the main frame such that the link can turn about a horizontal axis and at an upper end part thereof to a rear end part of the seat frame such that the link can turn about a horizontal axis, a second positive motion cam mechanism disposed between an upper end part of the link and the seatback frame and adapted to cause the link to turn in accordance with the turning motion of the seatback frame, and the second positive motion cam mechanism includes a second shaft movably inserted in the second cam holes disposed at one of the upper end part of the seatback frame and the second cam hole disposed at the other and movably inserted in the second cam hole.
It is preferred that the main frame is provided with an engagement member removably engaged with the link and adapted to positionally fixing the seatback frame to the working position by prohibiting the turning of the link at the time of engagement.
It is preferred that a lower end part of a shielding member is disposed at a forward end part of the main frame such that the shielding member can turn about a horizontal axis, the shielding member is adapted to shield a gap formed between a forward end part of the main frame and the seat frame or a seat cushion disposed at the seat frame, and an upper part of the shielding plate is connected to a forward end part of the seat frame such that when the gap varies in size in accordance with the displacement of the seat frame, the shielding plate is turned in accordance with the size of the gap.
A second form of the present invention is to solve the second problem and provides, therefore, a chair with a seatback comprising a seat capable of tilting between a working position and a relaxing position, a seatback capable of tilting in accordance with a tilting motion of the seat, and bias means for biasing the seat from the relaxing position side to the working position side, wherein the chair with a seatback further comprises a rotary damper (180) for restricting a high speed tilting of the seat at least in one direction between the working position and the relaxing position.
In this case, it is accepted that the rotary damper restricts a high speed tilting of the seat from the working position side to the relaxing position side but allows a high speed tilting of the seat from the relaxing position side to the working position side. It is also accepted that the rotary damper restricts a high speed tilting of the seat from the relaxing position side to the working position side but allows a high speed tilting of the seat from the working position side to the relaxing position side. However, it is preferred that the rotary damper restricts a high speed tilting of the seat in both directions between the working position and the relaxing position.
It is preferred that the rotary damper can be switched from one to another among a first state in which the rotary damper restricts a high speed tilting of the seat from the working position side to the relaxing position side but allows a high speed tilting of the seat from the relaxing position side to the working position side, a second state in which the rotary damper restricts a high speed tilting of the seat from the relaxing position side to the working position side but allows a high speed tilting of the seat from the working position side to the relaxing position side, and a third state in which the rotary damper restricts a high speed tilting of the seat in both directions between the working position and the relaxing position.
A third form of the present invention is to provided a rotary damper which is suited to be used in the chair with a seatback according to the second form or others, comprising an apparatus main body having a receiving hole, and a rotor relatively rotatably inserted in the receiving hole, the apparatus main body and the rotor are provided with partition wall parts for dividing an annular space, which is formed between an inner peripheral surface of the receiving hole and an outer peripheral surface of the rotor, in a circumferential direction and forming a plurality of pressure chambers, one of the partition wall parts including a pair of fixed wall parts which are disposed on either the inner peripheral surface of the receiving hole or the outer peripheral surface of the rotor such that the pair of fixed wall parts are located away from each other in a circumferential direction, and a movable wall part circumferentially movably disposed at a receiving space formed between the pair of fixed wall parts, a first communication path and a first flow-in path for communicating the receiving space with the pressure chamber adjacent to one of the fixed wall parts being formed between the receiving space and the pressure chamber, a second communication path and a second flow-in path for communicating the receiving space with the pressure chamber adjacent to the other fixed wall part being formed between the receiving space and the pressure chamber, when the movable wall part is in abutment with the one fixed wall part, the first flow-in path being closed but the second flow-in path being open, when the movable wall part is in abutment with the other fixed wall part, the first flow-in path being in open but the second flow-in path being closed, at least one of the first and second communication paths being provided with a resistor part for generating resistance against the flow of fluid.
In this case, the pair of fixed wall parts are preferably disposed at the apparatus main body.
It is preferred that the first communication path includes a first communication hole for communicating the pressure chamber facing the one fixed wall part with the receiving space, and the second communication path includes a second communication hole for communicating the fixed chamber facing the other fixed wall part with the receiving space.
It is preferred that the apparatus main body is movably provided with a first and a second adjustment member, which can be operated from outside thereof, such that the first and second adjustment members can be brought towards and away from opening parts facing the pressure chambers of the first and second communication holes, and a forward end part of at least one of the first and second adjustment members is brought towards the first and second communication holes, thereby forming the resistor part at least between the forward end part of the first adjustment member and an opening part of the first communication hole or between the forward end part of the second adjustment member and an opening part of the second communication hole.
Preferably, the first and second communication holes are formed in a row with axes thereof aligned with each other, and the first and second adjustment members are movably disposed in an axial direction of the first and second communication holes with axes of the first and second adjustment members aligned with axes of the first and second communication holes.
The first and second adjustment members are preferably threadingly engaged with the apparatus main body.
A fourth form of the present invention is to solve the third problem and provides, therefore, a chair with a seatback comprising a main frame, a seat supported by the main frame, and a seatback arranged at a location higher than a rear part of the seat and supported by the main frame through a support arm, wherein a pair of the support arms are disposed one at a left and the other at a right, and the pair of support arms are elastically deformable so that when a user twisted his body with his back pressed against the seatback, the seatback can turn in a horizontal direction following the twisting motion of the user""s body.
In this case, it is preferred that the seat is tiltably supported by the main frame for tilting between a working position and a relaxing position through a tilting mechanism, a pair of return springs are disposed between the main frame and the seat and adapted to bias the seat from the relaxing position side to the working position side, and end parts of the pair of return springs for biasing the seat from the relaxing position side to the working position side serve also as the support arms.
It is preferred that the tilting mechanism includes two pairs of front and rear turning links whose lower end parts are supported by the main frame such that the lower end parts can turn about a horizontal axis extending leftward and rightward and whose upper end parts are connected to the seat such that the upper end parts can turn about a horizontal axis extending leftward and rightward, a coiled spring is used as the return spring, and a pair of the coiled springs are arranged in a row between the pair of front turning links.
The main frame is preferably provided with a rotary damper for restricting a high speed turning of at least one of the two pairs of turning links.
It is preferred that the main frame is provided with an adjusting mechanism for adjusting biasing force of the coiled springs in accordance with turning operation of the adjustment member, and an adjustment member for operating said adjustment mechanism is disposed at a front end part of the main frame and at a front part of a generally central area of the pair of front turning links.